Trying Microsoft’s new Windows 10 Technical Preview Build 10051 on a Windows Phone is like drizzling honey over granola: It can be an excruciatingly slow experience that rewards you with a sweet, yet nutritious update.

Let’s say that again: Some aspects of the new build are slow. Even after a botched rollout earlier on Friday, Microsoft’s new software took seemingly forever to download and install. Now that the initial rush has been exhausted, your mileage may vary. But sometimes using the new OS build is literally a labor of love.

The new update adds support for the Project Spartan browser, plus new versions of several apps: Outlook Mail, Outlook Calendar, Phone, Messaging, People, and Maps. You’ll also find an improved basic Camera app, which pulls in some of the functions from the recent Lumia Camera update. Most are slow to load and use, especially Spartan and even parts of the core OS, at least on my Lumia 830.

Why this matters: The slow performance of the new build, and the delays preceding the rollout, raise questions about the state of the software. We all understand this is alpha code. At a time when Microsoft’s struggling for viability in the phone space, however, it’s taking a risk in drawing attention to subpar performance rather than Windows 10’s new functionality.

A surprisingly sluggish Spartan

Mark Hachman

Spartan, especially, is agonizing to use. It can take seconds before a page appears to load, and seconds more until the page actually becomes responsive. Part of that has to be due to how the browser handles all of the processes and code attached to modern Web pages, which is disconcerting given that Spartan was built from the ground up to handle such content. Reading a page in the the browser’s built-in reading mode speeds up the process, but there doesn’t seem to be a way to open a link directly in the reading mode—you can only reload an existing page.

Still, using Spartan feels natural and intuitive. About the only element that feels out of place is burying the additional tabs behind a menu at the bottom of the screen, although Windows Phone 8.1 also does this. I still like Android’s choice of placing the tabs icon at the top of the screen.

Microsoft has said it will replace Internet Explorer with Project Spartan in Windows 10 phones. At this point, that news seems daunting. But if Microsoft can give Spartan a kick in the pants, I think users will be happy.

Outlook Mail and Calendar: Excellent

From the ridiculous to the sublime: The new Outlook Mail and Calendar apps, meanwhile, are superb. Microsoft seemingly has dozens of variations on its core mail apps: there’s the basic Mail app in Windows 8.1, the Mail app on Windows, Outlook 2013, Outlook.com—the list goes on. On Windows 10 for phones, Outlook Mail ties your various inboxes into one nice package, and then integrates it with the Outlook Calendar app. (You can launch each app separately, but you don’t need to.)

Mark Hachman

Email is minimally presented. Your inbox is presented as a list of tiles: Swipe left to delete, swipe right to flag. By default, your emails are saved in conversation view, which you can expand by tapping on a tile. Once you open an email, all the options you’d want are listed in a row of icons at the top.

Mark Hachman

You can quickly jump to the calendar by digging through the menu at the upper left. Once in calendar mode, Outlook presents a rather nifty weekly view at the top, and an endless column of your appointments at the bottom. Hardly any tapping’s needed to navigate through your calendar; instead, it’s largely predicated on swiping right and left and down and up.

Phone and Messaging apps: Simple, uncomplicated

We spent just a few minutes with the Phone and Messaging apps, which look quite like what Microsoft showed off in Redmond in January. The user interface is almost too minimal, with a gray-on-black motif that’s a bit dull and difficult to read. Ditto for the Messaging interface as well.

Maps: Vibrant and useful

I’m also a fan of the new Maps app, one of the “universal” apps that bridge Windows 10 devices. At its core, the Maps app favors the simple look of Bing Maps. But start searching for nearby places of interest, and Bing suddenly shows you local restaurants with large illustrations and even a “streetsider” view.

Mark Hachman

Even with all this, Maps is fairly responsive, and a feature I’d like to see in my current Windows Phones, now.

People: Awfully drab

Mark Hachman

Microsoft crafted the new People app using the same look and feel as the Phone and Messaging app, and it’s an awfully somber backdrop for the most important people in your life. There’s also no apparent way to change the monochromatic background color. I think Microsoft could at least offer a setting to change the theme.

Camera: Well, that was unexpected

Nokia and Microsoft seemingly have dozens of camera and camera-related apps. Windows 10 Build 10051 takes a small subset of the recent Lumia Camera update and imports them into the generic Camera app. (Note that if you're upgrading from a previous build, you'll have to manually launch the Camera app, not the Nokia Camera app. And yes, Nokia Camera is different than Lumia Camera, which is also different than the Camera app.)

But if you've used the Lumia Camera app, you'll notice that the new Camera app uses the same interface, complete with the "wand" icon that normally launches the Rich Capture feature. Now, however, the wand icon simply turns on the HDR function.

In all, I came away from the new build with three impressions: First, some of Microsoft’s universal apps, including Maps and the new Outlook apps, are outstanding and should be considered among the selling points of the new Windows 10 for phones. Second, some of the color schemes need to be rethought. Microsoft may be quietly designing the UI for a Surface phone; if so, that needs to be better communicated. Finally, Microsoft needs to do some tweaking to improve performance—but its engineers undoubtedly know this.

As third fiddle in the OS space, however, I just wished for Microsoft’s sake that the company had pushed out the build earlier. Some elements need work, and some features are terrific, but they have yet to reach a mainstream audience.

This story, "Hands on: Windows 10 Build 10051 brings impressive new features to phones, but slowly" was originally published by
PCWorld.